The present invention relates to a process and a device for the control of the piecing process in a spinning device, such as an open-end spinning rotor.
It is known from German patent 25 07 199 A1 that the piecing process is controlled through contact-less measurement of the rotational speeds of open-end spinning rotors. The rotors are made with colored markings serving as reflectors. A photoelectric impulse receiver placed at a short distance and emitting a light ray receives the light ray reflected from the marking. In this manner, the momentary rotational speed of the rotor is scanned without contact, and the beginning of the piecing process is initiated as a function of the monitored piecing behavior of the spinning rotor. Impulses proportional to the rotor speed were used for the control of the piecing process, in particular to control fiber feed and yarn draw-off.
Further developments of this technical idea is that the rotor speed in open-end spinning devices is not measured directly, but rather that the speed of the bearing disks of the open-end spinning rotors is measured. In this case, the bearing disks were provided with reflectors for contact-less measurement of the rotational speed. Bearing disks of this type are known, e.g., from German patent 41 21 387 A1. Two reflectors are imbedded in suitable recesses in the surface of one face of the bearing disks. However, the optical measuring of rotational speed no longer provides reliable and clear signals in case of heavy fly from the fiber material to be spun.
This problem was solved by building small magnetic pins into the bearing disks (German patent 43 13 753 A1). In this design of a bearing disk, above all, care must be taken to insure above all that the bearing disks with the built-in magnetic pins should present as flat and smooth a surface as possible, so that neither high points nor low points are formed.
This care applies also to the attachment of reflectors on other bearing disks (German patent 196 20 377 A1). This is generally so because even a small imbalance results in enormous centrifugal forces at the usual rotational speeds, so that the bearing disk may be damaged or even destroyed. Extensive damage of the spinning devices is also unavoidable in that case.
The method of contact-less measurement of the rotor speed is based solely on the principle that a signal emitter transmits an impulse signal to an impulse receiver. As a rule, a frequency measurement or speed measurement of moving parts in the rotor (bearing disks), or of the rotating rotor, are made. If the method for measuring the speed is to be one with reflectors on the bearing disks, the signal emitter is made in the form of a light source. The emitted light is reflected in a pulsating manner as the reflector passes, so that an impulse receiver records the light impulse. If the bearing disks are provided with magnetic pins, it also means that the magnetic pins are designed as signal emitters producing magnetic field lines which produce an induction current in an impulse receiver. In either case, the impulse receiver, in principle, solely records impulses that are proportional to the rotor speed.
For this type of rotational speed measuring, the bearing disks necessarily require especially high fabrication quality. Furthermore, magnetic forces of the magnetic pins may magnetize other materials in the spin box susceptible to magnetization and cause additional interference. Under certain circumstances, the impulse emitter must be positioned precisely for the impulses to be counted by the impulse receiver. In addition, interference may be produced due to the fact that the spinning device is being soiled by fly during the spinning process.